Sheet piling wall without enough toe-in 1

[colombiu]

Hello to everyone

I am trying to design and analyse a sheet piling wall for a project. As the site has the presence of rocks the client has found out that in some points the rock is just 200mm below the excavation level. Due to the depth of the excavation and my soil parameters,the toe-in length required to make the system stable is of about 2.0m which in this case is not possible to achieve due to the strength of the rock as our sheet piles would not go through it.

My question is: Is there any possibility to provide further stability just installing an anchor or a prop right at the bottom of the excavation to provide a lateral restraint? As there is zero passive pressure, it would help the wall to prevent the toe-in from kicking out. Additional to this, is there any way to calculate the factor of safety for this arrangement? Support-IT is not able to calculate any factor of safety for this arrangement if there is not any support (fixed or free) at the bottom of the vertical element.

If my idea is insane and not applicable for this case, could you advise for other solutions that I can carry on?

I hope to hear from you soon engineers! Thanks for your assistance.

Juan

 

[PSlem]

Typically toe pins are used. Drill a diagonal hole, fill with grout, insert a rod, and weld it to a plate welded over the hole cut in the sheet pile.

 

[PEinc]

You really have not given enough information for us to give you a good answer. How tall is the wall? Is the wall a cantilevered wall or a braced or tiedback wall? How many levels of support? If braced or tiedback, how far below the top of the wall are the braces or tiebacks?
Don't just dig to the bottom of the SSP wall to drill and install pins, anchors, or braces. The wall could kick in or fall over before you install the additional support near subgrade.

http://www.PeirceEngineering.com

 

[oldestguy]

While waiting for more comments, do you have paper, pencil and a calculator? Since the program ( Support-IT is not able to calculate) won't work for this, how about doing it the old fashoned way where you know where the numbers come from?

Have you considered heavy duty sheets with tips? That may do the job along with more than the usual interior bracing.

http://www.piletips.com/Sheet_Pile_Drive_Points.htm

 

[colombiu]

Further information includes ...

- excavation level = 5.3m
- no groundwater
- 0-2m loose sand
- 2-4m hard clay
- <4m weathered sandstone
- bottom of sheet pile installed is 0.8m above excavation level.
- can not anchor

Please let me know if you have any suggestions about how to brace this sheet pile wall. The sheet piles have already been installed and unfortunately we were denied anchor permission.

 

[PEinc]

I assume that this wall is a relatively straight wall and not a closed cofferdam where you could use an internal bracing system. Therefore, if anchors are not allowed, you will need to install two tiers of wales with inclined raker braces and heel blocks. Because rock is above subgrade, you should also have the sheeting wall set back about 4 or 5 feet from the excavated rock face to allow a stable, benched rock cut at the base of the sheet piling. If you don't know what all of this means, it is time to hire someone who does know. This probably should have been a drilled-in soldier beam and lagging wall, braced at one level, unless you would be allowed to slope a few feet behind the wall. If you are trying to build an MSE wall in front of this sheeting wall, then you have bigger problems.

http://www.PeirceEngineering.com

 

[BigHarvey]

You could use a combi-wall (tubular piles + sheetpiles) where piles would be drilled in the rock (OD method) and sheetpiles stopped on the top of the rock layer.

 

[QAMaster]

I agree with PEinc, sounds like this should have been a soldier pile and lagging wall. You indicate there is no groundwater and adequate soil profiles. Why did you select sheet piles?